1. Technical Field
The disclosure relates to transducer arrays for producing sound, and more particularly to a high power sound source for use in liquids.
2. Description of the Problem
Sound is a disturbance in the physical properties of an elastic material/medium that propagates through the material. The disturbed physical properties can be alternation in pressure, the displacement of particles or a change in the density of the elastic material/medium. Sound in the form of an acoustic pressure wave will have alternating zones of high and low pressure, which can be referred to as the compression and rarefaction waves. An acoustic pressure wave propagating through a liquid medium can produce phase changes and otherwise affect physical properties of the liquid medium due to changing pressure. Pressure drops in a liquid medium can result in the liquid medium temporarily assuming a gaseous state, gasses dissolved in the liquid leaving solution, or both. In other words bubbles can form and collapse. Such bubbles are termed acoustic cavitation bubbles. Usually acoustic cavitation bubbles rapidly collapse, which in turn can produce intense shock waves.
Whether acoustic cavitation bubbles are a problem in a given situation depends upon the system. For example, in systems where the pressure variation is highest at the surfaces of the transducers acoustic cavitation bubbles occur along these surfaces and their occurrence decreases rapidly with increasing distance from the surface of the transducer. In such systems the transducer surfaces are vulnerable to damage from acoustic cavitation.
The acoustic cavitation phenomenon can also limit the amount of power that can be transferred from the transducer element(s) to the propagating medium and distort the resulting signal. A cavitation resistant array was proposed in U.S. Pat. No. 6,050,361 in which interstices of the sonar array between transducers was designed to match the specific acoustic impedance of water.
The present applicant has a pending United States Patent Application for an Omni-Directional Radiator for Multi-Transducer Array (Ser. No. 12/590,182, filed 4 Nov. 2009, which is incorporated herein by reference) which teaches use of a full or partial toroidal waveguide in sonar applications which limits cavitation for a given power input level. The radiator includes two facing interior surfaces forming boundaries. Acoustic transducers are arranged in a constellation along one of the interior surfaces of a waveguide to face the opposed surface. The facing interior surfaces extend outwardly from a central base or core of the waveguide and terminate at a mouth. Pressure waves propagating outwardly in the waveguide may be reinforced along a portion or substantially the full depth waveguide, including being summed in a cumulative or cascade manner, with operation of outer transducers being delayed and phase compensated to achieve coherent reinforcement of the pressure wave as it propagates outwardly from the core. The waveguide may be divided into channels by the use of interior radial baffles to increase output amplitude.